The invention is advantageously applicable throughout the field of radio location in all RF bands, and in particular in the HF, VHF, and UHF bands. In general, the antenna system of the invention is applicable to detection and surveillance, and in particular to anticollision device, e.g. between aircraft, and to warning devices. It may be installed fixed on the ground or it may be carried by a land vehicle, a ship, or an aircraft.
Radio direction finding applied to radiolocation is conventionally based on two known techniques: the Watson-Watt technique with an Adcock antenna; and the Doppler effect technique.
The Watson-Watt technique uses amplitude information in that the ratio of signal amplitudes from two orthogonal pairs of dipoles provides an approximation to the tangent of the looked-for angle of incidence. This method is not very accurate because of octant error, which error is also sensitive to the elevation angle of the incident wave.
The Doppler effect technique which requires a large number of radiating elements (e.g. 16 or 32 or even more) has low sensitivity because of the coupling between the radiating elements and above all it requires the radiating elements to be switched cyclically and at high speed. In addition, the relatively complex acquisition and processing electronics must be accurate and stable over time. Further, this technique requires in particular an auxiliary reference antenna for eliminating the phase modulation that is often present in the signals to be located.
Other techniques exist based on the known principle of interferometry. However all such techniques require a plurality of antennas to be switched.
Thus, the technical problem to be solved by the present invention is to provide an antenna system in accordance with the preamble that does not include a switching device, that provides good sensitivity and good locating accuracy, and that is compact.